Kudzu bugs’ impact on 2013 yields

Economic infestations of kudzu bugs in Alabama soybeans occurred for the first time in 2012 in scattered fields located mainly in northeast Alabama. The pest spread to additional fields in 2013 and an estimated 10,000 acres of soybeans were sprayed in 2013 mainly in east and east central Alabama.

Several tests were conducted in 2013 in central Alabama (Prattville and Shorter) to assess the impact of kudzu bugs on soybean yields. All the tests that compared yields in sprayed and unsprayed plots showed either statistically significant or numerical yield reductions in all unsprayed plots. Yield reductions ranged from one bushel to 11 bushels per acre. The 11 bushel yield reduction occurred in Group 4 soybeans planted April 22 that reached the R3 stage by 6/21.

The number of kudzu bug adults in this study per 15 inch diameter sweep-net sweep across two rows averaged 5.6 per sweep on 6/11 and 16/sweep on 6/21 and 7/1 in unsprayed plots. Applications of a pyrethroid insecticide to plots on one or more of the following dates; 6/12, 6/22, 7/3 and 7/26; showed that under test conditions 2 applications were needed (7/3 and 7/26) to maintain optimum profits.

Kudzu bugs continued to migrate into soybean plots up until the third week of July in Prattville in 2013 and test plots sprayed as late as July 11 saw a resurgence of adult kudzu bug numbers. The highest density of kudzu bugs detected in any test plot in 2013 was 76 per sweep on August 7 at Prattville in another study con-ducted to compare insecticide efficacy.

Spraying soybeans in late June and the first half of July reduced the number of immature kudzu bugs present during the last half of July and August since the sprays reduced adult numbers and thus fewer egg masses were deposited in sprayed plots. There was a trend toward fewer numbers of kudzu bugs infesting plots as the planting date changed from April and May to June and July. Other states report that since adults tend to aggregate on field edges, border sprays can, at times, be an effective management strategy that slows or prevents the movement of adults across a field. Several pyrethroid insecticides, orthene and carbaryl provide initial control of 80% or better.